After appearing in various variant covers Gwenpool much like Spider-Gwen took off. What was really amazing the Gwenpool phenomena is that she was'nt even featured in a comic, just on covers!

Chris Bachalo's variant cover Gwenpool's origin

She first appeared in Deadpool Secret Secret Wars #2 cover variant by Chris Bachalo. This cover started a craze for the character. The Gwen Stacey / Deadpool hybrid struck a chord with the fan base. Cosplayers began using her in Cosplays, fans wrote in letters and artists began drawing her. Marvel noticed it and now there will officially be a .........Gwenpool.

Gwenpool will appear in Howard the Duck #1 (November 2015) I think this will count as her First Appearance. Then she will appear in a solo series called Gwenpool Special #1 (December 2015).